Diabetes mellitus is strongly associated with microangiopathy and macroangiopathy and is a strong independent risk factor for cardiovascular disease and cardiovascular mortality [9]. Endothelial dysfunction which plays a crucial role in the atherosclerotic process is commonly observed in patients with diabetes mellitus and already prediabetes and has - amongst other factors - been linked to fasting and postprandial hyperglycemia. Taken into account that gliptins reduce hyperglycemia and hyperglycemic peaks by preventing inactivation of GLP-1, which exerted beneficial effects on the endothelium in previous studies it is of major interest whether therapy with gliptins improves endothelial function of the micro- and macrovasculature and thereby might prove to affect cardiovascular morbidity and mortality in diabetic patients in the long term. The retina offers the unique opportunity to directly visualize and investigate the microvasculature in vivo [10-14].